Generally, radioactive waste indicates material containing a concentration of radioactive nuclide at or above a specified level, or material contaminated with a radioactive nuclide.
According to subparagraph 18 of Article 2 of the Korean Nuclear Safety Act, radioactive waste is defined as “radioactive material or material contaminated with the radioactive material that should be disposed (including used nuclear fuel determined to be disposed according to subparagraph 35 of Article 4).
Radioactive waste is classified into high-level radioactive waste and intermediate/low-level radioactive waste depending on the radioactivity concentration and heat generation rate.
In subparagraph 1 of Article 2 of the Enforcement Decree of the Nuclear Safety Act, high-level radioactive waste is defined as radioactive waste having a radioactivity concentration and heat generation rate higher than those specified by the Nuclear Safety and Security Commission.
Further, in Article 2-1 of the Enforcement Decree of the Nuclear Safety Act, intermediate/low-level radioactive waste is defined as radioactive waste other than high-level radioactive waste.
According to Article 3 of the Nuclear Safety and Security Commission Notice (No. 2016-16), high-level radioactive waste and intermediate/low-level radioactive waste are classified based on a “radioactivity concentration of 4000 Bq/g of radionuclide emitting alpha-rays with a half-life of 20 years or more and heat generation rate of 2 kW/m3”.
Most of the radioactive waste is generated in a nuclear power generation process. For example, the radioactive waste is generated in mining, refining, conversion, enrichment, fuel fabrication of uranium, nuclear power operation, reprocessing, dismantling of nuclear power facilities, and the like.
Among those processes, the dismantling of nuclear power facilities indicates the process of dismantling nuclear power facilities of old nuclear power plants. This process includes a step of controlling access to main facilities after the decontamination of radioactive pollutants and the removal of the radioactive pollutants from the nuclear power facilities, and a step of dismantling and removing radioactive-contaminated facilities and structures in order to decrease the radioactivity level to a level in which a site can be used without limitation.
Recently, as the nuclear power plants in operation have grown older, the number of nuclear power plants at the end of their life span has increased. Therefore, there is a demand for a technique for processing the radioactive waste generated during the process of dismantling nuclear power facilities of nuclear power plants that have ceased operation. At this stage, a technique for dismantling and cutting nuclear power facilities is applied based on the characteristics of the particular nuclear power facility. For example, an underwater remote plasma arc technique is applied to various components of a reactor core, an underwater remote arc saw cutting technique is applied to a reactor pressure container, and a mechanical cutting technique and an abrasive water jet technique are applied to shielding concrete surrounding a nuclear reactor.
The radioactive waste generated at the radioactive waste generation site is stored in a container such as a special container, a drum, a large container, or the like, and then transported to a radioactive waste disposal site for isolated disposal. For example, the radioactive waste transported to the radioactive waste disposal site is isolated and disposed of in a surface disposal facility close to the ground surface or in a cave disposal facility underground by several tens of meters from the ground surface.
However, in the case of dismantling nuclear power facilities under water in order to improve radiation shielding efficiency, a radioactive waste container for storing the radioactive waste generated in the process of dismantling the nuclear power facilities should be positioned under water. Presently, it is considerably difficult to fasten a container body and a cover of the radioactive waste container under water.
Further, when a connecting portion, where the container body and the cover are made to be in contact with each other, is formed in a flat shape, there is a limit to how much the radiation emitted from the radioactive waste in the container body is shielded.
In addition, when storing the radioactive waste generated during the process of dismantling the nuclear power facilities under water, water flows into the container body positioned under water along with the radioactive waste. However, there is no device for draining the water flown into the container body. Therefore, the container body becomes excessively heavy and the radioactive waste storage efficiency is decreased.
Moreover, there is no device capable of lifting the radioactive waste container in which the radioactive waste is stored under water. Accordingly, it is not possible to stably lift the radioactive waste container in which the radioactive waste is stored under water and transport the radioactive waste container to the radioactive waste disposal site.